Curves from equasions

Variable Section Sweep using a circular trajectory and line section rotating about the trajectory. An edge of the resulting surface(s) will describe the 'garter spring' shape you describe.

If you do a bit of searching you should be able to find an example model.

... however if you prefer an 'equasion' ...

turns = 50 r_ = .25 theta = 360 * t r = 5 + r_ * cos(theta * turns) z = r_ * sin(theta * turns)

Thank you very much. The equasion was exactly what I needed. Peter

Super deal. ;^)

And a big attaboy to you for the quick and accurate response. It would have taken me a day of digging to come up with it. Except, by the time I logged on again to this NG, question asked AND answered. You can go to a lot of the "better", "more popular" Pro/e sites and NOT get responses this quick or at all. 41 minutes to a response; over night, EARLY A.M. (doing equations in noBadCAD's sleep) with the actual, detailed solution. Hat's off, this effort was in the true spirit and best practice of this NG!!

David Janes

UVZ snipped-for-privacy@yournetplus.com...

ve taken me a day of digging to come up with it. Except, by the time I logg= ed on again to this NG, question asked AND answered. You can go to a lot of= the "better", "more popular" Pro/e sites and NOT get responses this quick = or at all. 41 minutes to a response; over night, EARLY A.M. (doing equation= s in noBadCAD's sleep) with the actual, detailed solution. Hat's off, this = effort was in the true spirit and best practice of this NG!!

A very prompt reply indeed and thanks again. As a point of interest, this equasion will produce the required curve in both WF3 and WF4 (the only two versions that I have access to). However when I try a variable section sweep using this curve as the trajectory, in WF4 it works perfectly, but in WF3, it won't work. Even when the sweep shape is a simple circle, it fails. I have noticed this with a few other equasion curves when using them as a trajectory for a sweep in WF3. When it fails a right click over the error box shows a greyed out "Trajectory error". They must have fixed this in WF4. Peter

That's interesting. I use WF2 which exhibits the same behavior you noted in WF3. The problem is, I believe, rooted in the "minimally twisted" Automatic Horizontal / Vertical Control* (compounded when creating a closed loop?). Another algorithm that could be employed is to maintain alignment to the traj curvature vector (which falls down when vector length is zero but special 'minimum twist' handlers can be employed there too).

• Ref VSS Help. It's an interesting exercise to show a curvature graph / comb for a trajectory then sweep a line segment and compare results.

For the 'garter' curve being worked with there are (at least?) a couple of 'fixes'. One is to use the original suggestion of creating the helical curve by sweep a rotating line segment along a circle and then using the resulting helical ribbon's edge chain to sweep the model geometry section. The ribbon surface normal will be the default Y vector orientation reference. Another option is to duplicate the helical curve by equation using a larger "r_" value and use that curve as an X vector reference.